Cancer immunology is the study of interactions between an immune system and cancer cells such as, tumors or malignancies. The initiation of an immune response, such as recognition of cancer-specific antigens, which are expressed by human tumors and not in normal tissues, is of particular interest. Generally, methods to control the division and proliferation of the malignant cells have been to isolate these antigens and present them so that they are recognized by the immune system as non-self antigens and induce a specific immune response.
There are a significant number of growth factors identified at present, and most, if not all, have been shown to be important mediators of cell proliferation in various cancers in addition to being implicated in other disease conditions. Generally, growth factors are soluble serum proteins that recognize, and are bound by a group of growth factor receptors located on cell surfaces. Particular growth factors may be specific for a single receptor, or may bind to more than one closely related receptor with varying affinities. Similarly, some receptors bind only a single growth factor ligand while others can bind to multiple related growth factors, again usually with differing affinities. Upon binding to its natural receptor, the cytoplasmic domain of the receptor is phosphorylated, and this initiates an intra-cellular signaling cascade which results in modulation of transcription of one or more genes and ultimately to progression through the cell cycle and cell proliferation.
Growth factors and their receptors are essential components of the normal processes of growth, development and repair, and their tissue distribution profiles and expression levels closely regulate cell growth. Numerous studies have shown that growth factors can stimulate proliferation of a variety of cell types both in vitro and in vivo (Cohen S., Carpenter G., PNAS USA 72, 1317, 1975, Witsch E et al: Physiology: 25(2):85-101, (2010)). Moreover, certain growth factors have been shown to stimulate proliferation in some cancer cell lines, for example epidermal growth factor (EGF) can stimulate some non-small cell lung carcinoma cells (Osborne C. K. et al. Can Res. 40, 2, 361 (1980)). Other growth factors such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF) are important in several oncology diseases, such as non-small cell lung cancer (NSCLC) (Ballas M S, Chachoua A., Onco Targets and Therapy: 4, 43-58 (2011)), Prostate cancer, (Cox M E et al; Prostate 69 (1):33-40 (2009)), and Breast cancer (Law J et al, Cancer Res; 68, 24:10238-10346 (2008)).
High levels of various growth factor receptors have been reported in malignant tissues. For example, the epidermal growth factor receptor (EGFR) has been detected at unusually high levels in malignant tumors of epithelial origin, such as lung, breast, bladder, ovarian, vulva, colonic, pulmonary, brain and oesophagus cancers. The role played by growth factors and their receptors in regulating tumor growth is unknown, but there are suggestions that growth factor receptor expression in tumor cells provides a mechanism for autocrine growth stimulation which leads to uncontrolled proliferation (Schlessinger J., Schreiber A. B., Levi A., Liberman T., Yarden Y. Crit. Rev. Biochem. 1983, 14 (2) 93-111). Further, Liao Y et al; Hum Pathol 36(11):1186-1196 (2005) and Cox M E et al; Prostate: 69(1) 33-40 (2009) describe the role of increased Insular receptor and growth factor on metastatic prostate cancer.
One treatment strategy to target growth factor signaling in cancer therapy has been to use a passive immunotherapy, such as using monoclonal antibodies against the particular receptor/receptors involved. Such studies have demonstrated that the specific recognition by an antibody of the receptor that is able to inhibit the binding of the ligand can have an inhibitory effect on the mitogenic stimulation of malignant cells (SATO J. D., et al. Methods in Enzymology, vol. 146 pp 63-81, 1987). However, antibodies which are of murine origin will usually produce a human anti-mouse antibody response (HAMA), thus limiting them to a single administration.
Other treatment strategies have been to use an active immunotherapy with vaccines that contain the growth factor of interest to induce an immune response against the molecule to inhibit the proliferation effect of the growth factor on tumors. U.S. Pat. No. 5,984,018, to Davila et al., entitled Vaccine Composition Comprising Autologous Epidermal Growth Factor or a Fragment or a Derivative Thereof having Anti-tumor Activity and use Thereof in the Therapy of Malignant Diseases, discloses, for example, the use of a vaccine that contains a mixture of a growth factor and an immunogenic (i.e. non-human) carrier protein chemically conjugated together using gluterhaldehyde. However, without being bound to any particular theory it is thought that chemical conjugation hinders immune responses against the vaccine.
This is a technically challenging approach, as it requires that the host generates an immune response to a ‘self antigen’, and vertebrate immune systems have evolved to prevent such responses occurring. Where a strong immune response is generated against a self antigen, for example, one that includes T-helper cell activation, an auto-immune disease state usually results. For many years it has been hypothesized that some auto-immune disorders, for example, lupus, multiple sclerosis (MS), diabetes etc., might be caused by early exposure to an environmental agent that includes immunogenic epitopes (T-cell epitopes) that closely mimic host self-epitopes. This could lead to the stimulation of T-helper cells that are cross reactive with host epitopes. Subsequent exposure to the environmental agent could then result in an anti-self immune response (Albert, L. J., and Inman, R. D New England Journal of Medicine, December 30th pp 2068-2074, 1999). It has since been demonstrated that a viral antigen can indeed generate an anti-self immune response against a nerve cell protein (Levin, M. C. et. al., Nature Medicine vol 8 (5) pp 509-513, 2002).
U.S. Publ. No. 2006/0251654, to Casimiro et al., entitled Method for Treatment of Malignant and Infectious Chronic Diseases, (the '654 publication) discloses a method of treating a subject bearing a malignant or infectious chronic disease comprising the method of immunizing the subject with a vaccine containing a self antigen associated with the malignant or infectious chronic disease that is coupled to a carrier protein; treating the subject with an immune modulator agent; and immunizing the subject again with the vaccine of the step 1, and an appropriate adjuvant selected from aluminum hydroxide and Montanide ISA 51 (Seppic, Paris, France). Unfortunately, the preparation of the vaccine by chemical conjugation is thought to hinder the immune response.
The majority of the vaccines described above exhibit a number of limitations, arising primarily from the method of manufacture and the potential lack of uniformity and homology of the protein product. The vaccines described above generally comprise a mixture of a recombinant carrier protein and polypeptides of human origin that are chemically conjugated using gluterhaldehyde. Unfortunately, this reactive reagent can undesirably form covalent cross-linking bonds between varieties of chemical groups, and generally leads to a highly heterogeneous product. Thus, the resulting vaccines may comprise not only carrier protein molecules with varying numbers of the target human polypeptide attached (for example, 0, 1, 2, 3 etc.), but the human polypeptides can each be attached to the carrier via different atoms and so in different positions and in different orientations. Furthermore, both the target polypeptide and carrier protein molecules may be conjugated to themselves, resulting in various homo-multimers that may have no clinical efficacy and may not contribute to an anti-cancer patient immune response.